* lily/lily-guile.cc (robust_scm2double): new function. Use throughout.

* lily/lily-guile.cc (robust_scm2double): new function. Use throughout.

* lily/hairpin.cc: use Line_interface

* lily/tuplet-bracket.cc (make_bracket): use Line_interface.

* lily/mensural-ligature.cc (brew_flexa): replace horizontal_slope
() with beam ().

* lily/beam.cc (position_beam): new function
(brew_molecule): make sure that positions are calced before making
the molecule.

* lily/beam.cc (brew_molecule): fix beam offsets: overlap with the
stem do avoid small dents.